The US Department of Energy (DOE) Fuel Cell Technology Office (FCTO) has released the latest edition of an annual report showing that the average fuel economy of fuel cell electric buses from three fleets is 6.8 miles per diesel gallon equivalent (DGE) (ranging from 5.56 - 7.71 DGE), 1.4 times higher than conventional diesel buses (~4.2 miles per DGE) from one fleet and up to 1.9 times higher than compressed natural gas buses (~3.3 miles per DGE) in another fleet.
This demonstrates significant fuel economy improvement toward the DOE and Federal Transit Administration’s (FTA) target of 8 miles per DGE. FCEB durability has reached 23,000 hours, surpassing FCTO’s 2016 target of 18,000 hours, and range has reached up to 340 miles (547 km), more than 13% above the 2016 target of 300 miles (483 km).
However, NREL also noted that the fuel economy for the FCEBs has shown a decrease over time. This could be due to a variety of factors including changes in duty cycle, temperature, operator driving styles, fuel cell power plant degradation, and hydrogen station metering differences.
The report, entitled Fuel Cell Buses in US Transit Fleets: Current Status 2016 and published annually by the National Renewable Energy Laboratory (NREL), summarizes the progress of fuel cell electric bus (FCEB) development in the United States and discusses the achievements and challenges of introducing fuel cell propulsion in transit.
The 2016 report focuses on the August 2015–July 2016 time period for three demonstrations:
- the Zero Emission Bay Area Demonstration Group;
- the American Fuel Cell Bus Project at SunLine Transit Agency in California; and
- the American Fuel Cell Bus Project at the University of California at Irvine (UCI)
The results for these buses account for more than 550,000 miles (885,139 km) traveled and 59,500 hours of fuel cell power system operation.
NREL considers these FCEB designs to be around technology readiness level (TRL) 7—i.e., full-scale validation in a relevant environment. At this point in development, capital and operating costs for FCEBs are still much higher than those of conventional diesel technology. NREL noted that this is to be expected considering diesel is a very mature technology (TRL 9) and FCEBs are still in the development stage.
The fuel cell bus manufacturers continue to make significant progress toward meeting the durability target. In the 2015 report, NREL documented a single fuel cell power plant surpassing the 2016 target. At the end of the analysis period for this report (July 2016), that fuel cell power plant had reached 23,000 hours, nearing the ultimate target of 25,000 hours. A second fuel cell power plant has now surpassed the 2016 target, achieving 18,293 hours. Of the 18 fuel cell power plants included in the data set, 67% (12) have surpassed 13,000 hours of operation. The average hours accumulated is 12,302.
Despite the continued improvements in performance, fuel cell buses still face challenges to commercial viability, including:
Parts supply. Two of the agencies continue to experience some issues with availability of bus components that have a long lead time for delivery. This has improved over time as the project partners have learned what should be kept on hand. In some cases, bus components for the FCEB model are different from that of the diesel model so the bus parts inventory cannot be shared. The industry needs to further develop a robust supply chain or more shared components for these advanced components for FCEBs (as well as other electric drive buses).
Bus range/low fuel. AC Transit has reported that real-world bus range is lower than expected. Several factors contribute to the issue including operator familiarity and comfort level with the system, the fueling process, and differences in fueling rate between the two hydrogen stations. The flow rate of the station has an impact on the amount of hydrogen delivered to the tanks. The agency is addressing this challenge through continued training for operator and maintenance staff. It is difficult to measure real-world range because transit agencies typically fill the buses each day, regardless of the amount of fuel left in the tank. Over the last year, the average fill amount is 22.4 kg for the three evaluated fleets. This amount is less than 60% of the tank capacity. The buses are averaging 121 miles per day. This is more a function of how the buses are scheduled as opposed to the actual capability of the bus, NREL observed.
Maintenance staff. All transit agencies are experiencing issues with turnover of the most experienced staff through retirements or job changes. Fewer people are entering the field of technical repair, making new candidates scarce. This is particularly challenging for agencies with advanced technology buses, because technical schools are just now beginning to develop courses to handle maintenance and repair of these new technologies. Once these courses are available, there will be a lag time before graduates are ready to enter the market.
Maintenance costs. Maintenance costs for advanced-technology buses typically start low because the buses are under warranty and the manufacturer is covering the cost and taking an active, on-site role in troubleshooting and repair. Costs begin to increase as transit staff takes on more of the maintenance responsibilities and begins the learning curve to understand how to fully maintain the buses. As the staff becomes more proficient, the costs eventually stabilize. The transition of knowledge from the manufacturers to the transit staff is essential to commercializing the technology.
Purchase cost. The capital cost for FCEBs in 2010 was around $2.5 million. More recent orders for FCEBs have had an average cost of $1.8 million—a 28% decrease. Costs should continue to drop with increasing orders; the industry projects an order for 40 buses could result in costs closer to $1 million each.